Higher frequency electrical signals are becoming a requirement of new electronic equipment, such as personal computers, mobile communications, including cellular telephones and wearables, self-driving vehicles, including cars and trucks, and aviation devices, including manned and unmanned vehicles, including airplanes, drones, missiles and space equipment including satellites, spacecraft, space stations and extra-terrestrial habitats and vehicles. When electrical signals on the order of 10 MHz are passed through conventional copper foils, the signal path is generally through the body of the copper foil as illustrated in FIG. 1. The current is able to tunnel below the surface profile and through the bulk of the conductor. However, when the frequency of the electrical signal is increased to 100 MHz or greater, the influence of the skin effect in which current flows only through the surface of the conductor becomes remarkable, as illustrated in FIG. 2. Here, the current is forced to follow every peak and trough of the surface profile increasing both path length and resistance.
In manufacturing electrolytically deposited copper foil, a drum rotates about a horizontal axis, with a lower portion of the drum immersed in a liquid electrolytic bath. The electrolytic bath comprises a solution including copper. When an electrical current is applied through the bath, utilizing an insoluble metal anode, with the drum acting as a cathode, the copper in solution plates upon the outer surface of the drum and can be separated from the drum in the form of a copper foil as shown in FIG. 3. The electrolytically deposited copper foil conventionally is described as having a “drum side” (i.e., that portion of the copper foil that was adjacent the drum during foil formation). This “drum side” has occasionally been referred to in the art as the “shiny side.” The side of the electrolytically deposited copper foil opposite the drum side is called the “deposit side” (also sometimes called the “matte side” by persons in the art because, unlike the drum surface, which the drum side of the copper foil mirrors, the “deposit side” engages no solid surface during its formation but is subject to the liquid electrolytic bath during its formation. Therefore, the deposit side is generally more irregular in surface configuration than the drum side, as schematically illustrated in FIG. 4. This irregularity is termed “surface roughness” and can be measured. As used throughout this specification and claims, surface roughness is measured and provided as Rz standard, although there are other systems available to measure surface roughness. Not all measurement systems of surface roughness are equivalent. According to this standard, the results are presented as an average of 10 points.
A normally treated copper foil for incorporation into a copper clad laminate (a precursor to a PCB) has nodules added to the deposit side to aid in the adherence of the copper foil and polymeric component, which copper foil becomes laminated to the polymeric material of the copper clad laminate. The deposit side of the copper foil which engages the polymeric material is termed the “lamination side” as schematically illustrated in FIG. 5A. As schematically illustrated in FIG. 5A, the nodules will tend to deposit on the elevated portions (“peaks”) of the surface irregularities of the deposit side of the copper foil. The opposing side of the copper foil (i.e., the drum side of the copper foil opposite the lamination side) is called the “resist side” because a resist, formed into a pattern, is placed upon the resist side of the copper foil to be etched by an acid or alkaline solution to remove portions of the exposed portions of the copper foil (i.e., the portions of the copper foil not covered by the resist) to form the printed circuit of the PCB. However, as can be readily seen in FIG. 5B, the electrical signal path is greatly attenuated when the skin effect of high-frequency signals on the order of 100 MHz or greater are attempted to be flowed through a copper foil which has been nodule treated on the deposit side of the copper foil, and any PCB incorporating the same, in the prior art due to the skin effect.
Thus, the prior art lacks an efficient way of transmitting high frequency signals on the order of 100 MHz or greater through a copper foil, PCBs and electronic products incorporating the same.
The embodiments described herein provide solutions to this long felt need of the prior art.